Control of wax deoiling



Oct. 18, 1955 D. c. ROBERSON ETAL 2,721,165

CONTROL OF WAX DEOILING Filed July 9, 1951 3 Sheets-Sheet l WAVELENGTH"'2 19 Q O O O 0 V o o INVENTORS LLIAILEIHOSGV DONALD C. ROBERSON 8|WARNER E. SCOVI LL BY WWJQQLPW I'M/r ATTOENEY5 FIG. I.

Oct. 18, 1955 D. c. ROBERSON ET AL CONTROL OF WAX 020mm 3 Sheets-Sheet 2Filed July 9, 1951 msmoo no "l. DONALD c WARNER E BY Wu,

fien- ATTOQNEK? Oct. 18, 1955 D. c. ROBERSON ET AL 2,721,165

CONTROL OF WAX DEOILING Filed July 9, 1951 3 She 3 SWEATING TIME, HOURS.

BHLVBMS m XVM NI no 1M INVENTORS DONALD C. ROBERSON 8 WARNER E. SCOVILL.

[be/r ATTORNEYS.

FIG. 3.

United States Patent CONTROL OF WAX DEOILING Donald C. Roberson,Warrensville Heights, and Warner Scovill, Lakewood, Ohio, assigors toThe Standard Oil Company, Cleveland, Ohio, a corporation of OhioApplication July 9, 1951, Serial No. 235,842

2 Claims. (Cl. 196-20) The present invention relates to a method ofdetermining at any time in the de-oiling of wax the oil content of thewax and thereby of controlling the de-oiling of wax in a manner toassure obtaining a finished wax product having a predetermined low oilcontent.

De-oil'mg of oil-wax mixtures is generally accomplished in either of twoconventional manners. The most common method is known as sweating inwhich oil is removed or sweated from a batch of the crude wax stool: byslowly raising the temperature of the wax in a container and draining05: the exuded oil until only a desired amount of oil remains in thewax. Another method is the removal of undesirable oil by means ofsolvent extraction. While the present process is applicable to eithertype of operation, attention is directed foremost to the sweating typeof operation since it presents particular problems of obtaining uniformsamples of wax for observance in determining the point at which toterminate the de-oiling treatment.

Wax sweating operations have generally been carried out in one of twotypes of apparatus. These are the pan and the tank sweaters. In each ofthese types, the method is substantially the same and involves chillinga warm molten liquid oil-wax mixture to a semi-solid state and thenslowly raising the temperature, during which time a liquid which isknown as foots oil, drains 0E the stock in the sweater. The desired waxproduct remains in the sweater.

In the present discussion and claims the oil content is determined bythe standard ASTM test method D72l-49 described in the American Societyfor Testing Materials Handbook (1949), page 981, in which the oilcontent is defined as the amount of a sample which is fiuid at -25 F.when in solution with methylethylketone.

It requires an experienced operator to know at what time a sweatingoperation should be terminated and the wax removed from the sweater. Itis impracticable to remove and analyze samples of the wax remaining inthe sweater at intervals during the process, not only because of theinaccessability thereof but also because of a sample taken from anyparticular location in the sweater is not necessarily representative ofthe remainder of the wax. It is, therefore, the usual practice toanalyze successive samples of the foots oil which drains from the wax.

One method employed by experienced operators is that of pouring a sampleof the foots oil into a melting-point wax bath, allowing it to cool andsolidify so that a cake of wax about 7" x 1 /2" x 1 /2" is formed, andexamining the cake by transmitted light. If the operator observes agreenish tinge, it indicates to him that the wax in the sweater requiresfurther sweating. Experience has taught operators that the absence ofthe greenish tinge is indicative of a product which possesses desirablecolor and color stability and also has or approaches the proper meltingpoint. The absence of a tinge also indicates a low oil content which inturn provides a product of desirable tensile strength. If the samplecake is substan- Patented Oct. 18, 1955 ICC tially colorless, theoperator then determines its melting point by a suitable method such asthe ASTM method D87-42 described in ASTM Standards Handbook (1949), page698 or the Saybolt procedure. If the melting point meets thespecifications, the operator will then terminate the sweating operation.

It has now been found that the oil content of the wax in the sweater maybe readilyand easily determined at any particular time by determiningthe absorptivity of a sample of the foots oil at a particular wavelengthof light as explained more fully below. Thus, it is observed that whenthe absorptivity of oil-wax mixtures for ultraviolet (u. v.) lighthaving wavelengths between 240 and 350 millimicrons is plotted againstthe wavelengths, each oil-wax mixture will have a characteristic peakabsorption at a particular wavelength somewhere within that range, i.e., it will absorb a greater amount of light of that particularwavelength value between 240 and 350 millimicrons than it will at higheror lower wavelengths within that range. This absorptivity peak may occurat a difierent wavelength for different oil-wax stocks but always occursat the same wavelength for different oilwax samples taken from stocks ofthe same type and source. It has also been found that there is acorrelation between the numerical value of absorptivity of the foots oilfor light of that particular wavelength and the oil content of the waxin the sweater; that is, there is a direct relationship between the oilcontent values of the wax in the sweater and the absorptivity values atthe peak of absorptivity for various foots oil samples. This makes itpossible, in accordance with the invention, to determine the u. v.absorptivity of foots oil samples (a simple and quick procedure) andfrom the determination to ascertain the oil content of the wax in thesweater. In this way, the sweating can be terminated when the oilcontent of the wax in the sweater reaches a desirably low figure. Such aresulting wax of low oil content will possess desirable properties ofimproved tensile strength, and color stability. Thus an oil-wax stockcan be readily sweated to a predetermined value below that initiallycontained in the stock or to an oil content less than some specifiedvalue, such as 5 per cent. The same determination may be made of the oilremoved by solvent extraction after the oil is recovered from thesolvent and the oil content of the wax obtained from a similar but notnecessarily identical correlation, as more fully explained below. Thisprocedure and control for sweating operations is described below inconnection with the drawings inwhich:

Figure 1 is a graph, illustrating the absorptivity values at variouswavelengths of light of an oil-wax stock and showing the characteristicabsorptivity peak of the particular wax;

Figure 2 is a graph on logarithmic plot illustrating three relationshipsbetween (a) absorptivity versus oil content of successive samples of afoots oil stream from a particular stockcurve R; (b) absorptivity versusoil content of wax within the sweating equipment from the samestock--cuive R; and (c) absorptivity of the foots oil stream versus theoil content of wax in the sweater from indentical stockcalibration curveT; and

Figure 3 is a plot of time of sweating versus oil content of wax insweater.

The respective relationships illustrated in Figure 2 are plotted onlogarithmic scale purely for convenience in the conventional manner torepresent the relationships as straight line curves. It will be readilyappreciated that the same relationships could be represented by a curveon a linear scale.

Referring to Fig. 1, the absorptivity values (a) were calculated fromdata observed for a number of settings of a spectrophotometer using asample of a foots oil ciprocal of the transmittance that is, the ratioof the rate at which energy is transmitted in a beam of radiant energy(e. g., ultraviolet light) through a sample of the solution to the rateat which radiant energy is supplied to the sample; is the concentrationof the sample solution in grams per liter; and l is the length incentimeters of the sample through which the beam of light passes.

A definite absorptivity peak was observed at a particular wavelengthwhich is readily ascertained from a plot of the data as shown in thediagram plotted as Figure 1. It was observed that a peak of absorptivityoccurred at the same wavelength for a number of samples of the sweatstream from the same type of wax stock.

The ASTM weight per cent oil content was determined for the same footsoil samples on which the absorptivity was computed. A plot of theabsorptivity values of the foots oil samples at the peak wavelength,when plotted against the ASTM oil content of the samples foots oilgives. a smooth curve. When plotted on a logarithmic scale the curve isa straight line curve such as curve R of 'Fig. 2 (absorptivity values ofsweat stream versus oil content of sweat stream).

From the same control batch of wax, the absorptivity values of a seriesof sweated refined wax samples containing various observed amounts ofoil in the sweated product were likewise determined and plotted on thesame logarithrnic plot against the oil content; this plot was also astraight line curve (R') which was found to be on the same line as curveR but falling at lower values of percentage oil content as shown in Fig.2 as curve R. This curve of absorptivity versus oil content of the waxbeing a lower extension of the curve of the absorptivity versus oilcontent of the sweat stream taken from the same type of stock in asweating operation, demonstrates the direct relationship between theproperties of the foots oil stream and the wax within the sweater fromwhich the foots oil is taken. The curves R and R actually may be joinedand extended at both ends as illustrated in Fig. 2. The resulting curveRR' (consisting of the sections R and R and extrapolations) isdesignated in the balance of the disclosure as the u. v. curve andpoints read from the curve are u. v. oil content. These values from theu. v. content curve are more nearly accurate for all correlations thanthe calculated values of ASTM oil content since the factors throughwhich errors may be introduced in the ASTM test method far exceed thoseof the present spectrophotometn'c determinations. Thus the necessity ormaking a quantitative separation which is diflicult and time consuming,measuring the wax sample only to one-tenth of a gram, dissolving thesample in methylethylketone, taking a sample at a specified temperaturefrom a body of wax of continuously changing temperature, and other stepsin the ASTM test method introduce errors. On the other hand, in thespectrophotometric system there is no necessity for such separation, thesample is weighed to the fourth decimal place and is diluted andtransferred but once (into the spectrophotometer cell). Furthermore, theoperator need measure only one physical property in this latter method.Experience has shown that the measurements are more accurate and thehandling of the sample simplified with resulting smaller chance forerror.

Furthermore, a third plot on the same logarithmic paper of values ofabsorptivity of the foots oil samples versus the oil content of the waxremoved from the sweater at the same time for different sweatingoperations on the same stock (for example, at the cut pointsthat 'is,the points at which sweating of several difierent batches of the samestock is terminated) also gives a straight line curve, such as curve Tof Figure 2, which is found to be parallel to both curves R and R above.This is done for a series of samples of wax to obtain values ofabsorptivity of foots oil samples versus oil content of wax todemonstrate that a plot of these values is also directly related to bothof the curves R (absorptivity versus oil content of foots oil samples)or R (absorptivity versus oil content of wax in sweater). The proprietyof the parallel relationship between curves RR' and T is furtherstrengthened by numerous other observations in which the oil-wax stocksare first treated by various refining procedures such as acid-treatingto reduce the aromatic content and then the absorptivity versus oilcontent relationships observed. The respective curves are always inparallel relationship, being displaced to the left. The degree of shiftdepends upon the nature of the treatment. The curve T is now establishedas a base calibration curve for other batches of stock of the same type.

It follows therefore, that, for any subsequent sweating operation upon adifferent batch of stock of the same type as the control batch only asingle point of absorptivity of foots oil versus oil content of wax inthe sweater need be observed. This pair of values may preferably betaken at the cut point of a preliminary sample sweat. The locus of thatpoint (absorptivity values of the foots oil versus the oil content ofthe wax) on a graphic plot will be on a calibration curve T for thatparticular batch of wax stock, which curve T is,

as shown, parallel to either of the curves R or R, above. Thus a curve Tmay be drawn through the single determined point and parallel to eitherof the curves R or R and this curve T will be the calibration curve forsubsequent portions of the same batch of stock. The simplest of the twopossible curves (R and R) to determine will, of course, be the one ofabsorptivity versus oil content of the foots oil sample (R) and thus thepoints on curve R will ordinarily be determined. The calibration curve Tcan then be drawn through the single point parallel to the predeterminedcurve R. The oil content of the wax is the sweater at various pointsbefore the out point can be also determined by reading from curve T thevalue opposite the observed absorptivity of the foots oil sample takenat that point.

The operator may now quickly determine the oil content of the wax in thesweater at any time during the sweating operation of all portions of thebatch subsequent to the preliminary run by the expedient of observingwith the aid of a spectrophotometer the absorptivity at a particularwavelength of light of a foots oil sample and, by reference to theestablished calibration curve T, can know the oil content of the wax inthe sweater. He will then be able to know the point in the operation atwhich to terminate the treatment. In conducting the sweating operation,the operator is also enabled to know in advance, by reference to thecalibration curve, the value of absorptivity of the foots oil stream towatch for in order to obtain a finished wax of the predetermined anddesired 'oil content.

Similarly, with a wax stock from a different crude source, a calibrationcurve may be established by determining the Wavelength at which thecharacteristic absorptivity peak is found, then running a preliminarysweat of a sample, determining the absorptivity at the peak wavelengthand oil content of a series of foots oil samples, plotting and drawing acurve through these values, determining the oil content of the wax atthe cut point of the control sweat, plotting and drawing a curveparallel to the first curve through the point represented by theabsorptivity of foots oil'and oil content of wax (both at the cutpoint); the latter curve is then the calibration curve for thatparticular wax stock.

Similar development of a calibration curve and its utility, incontrolling the de-oiling operations may be made for solvent de-oilingoperations wherein the absorptivity of the oil extracted from oil-waxmixtures may be observed.

The present invention, therefore, provides a method of determining theoil content of wax during de-oiling operations and a method of de-oilingoil-wax mixtures wherein control over the method is exercised bydetermining the absorptivity of successive samples of the foots oil orextracted oil for light at an observed characteristic wavelength between240 and 350 millimicrons. It is possible, by means of this controlmethod, to control the de-oiling operation with such precision that theoil content of the wax being tie-oiled, when the operation isterminated, will be within 0.05 of the amount desired. Thus, thede-oiling operation can be observed at regular intervals and terminatedwhen the oil content of the wax is found to be of a predetermined andcommercially acceptable value.

The reason for the agreement between the correlation of the absorptivityvalues of samples of the foots oil or extracted oil and the oil contentof the refined wax is not entirely understood but it may be surmisedthat the aromatic content of the oil in the wax and in the oil samplesaccounts for the peak values of absorptivity and that there are at alltimes aromatics present in the oil content to give the characteristicpeak. However, regardless of any theory the discovery provides anadequate and advantageous method for controlling the de-oiling of waxstocks in the preparation of refined waxes of any desired final oilcontent.

The method of control may be carried a step further using as a basis thesystem disclosed herein. The time interval between the beginning of thede-oiling operation and the taking of the respective foots oil orextracted oil samples can be recorded and, as each sample is examinedfor determination of the oil content of the wax, these values may beplotted as in Fig. 3time versus oil content. From a plot of a series ofsets of values a smooth curve may be drawn as illustrated in Fig. 3. Byextrapolating the curve a fairly accurate time may be rapidly estimatedfor the termination of the de-oiling operation and samples of the footsoil or extracted oil may be taken and observed at more frequentintervals as the time for termination of the treatment approaches sothat the most desired point for the oil content of the refined wax andthus for the termination of the de-oiling operation may be observedclosely. Here the relationship is plotted on linear scale although, ifdesired, it can also be represented on a logarithmic scale.

The method of this invention has many important advantages. Not only isthe method of control more accurate than methods heretofore known but itis also much faster and simpler. The ASTM method for determining the oilcontent of a parafiin wax requires from 3 to 8 hours. An analysis of theoil samples for absorptivity of ultraviolet light of a given wavelengthand thereby the oil content of the wax in the sweater in accordance withthe present invention requires only about 20 to 30 minutes. Not only isthe operator enabled to know the time at which the wax in the sweaterwill meet the desired and predetermined specifications of oil contentand thereby tensile strength for the commercial trade, but he can knowthe proper time to terminate the operation in order that loss ofdesirable wax will be minimized in the oil stream being withdrawn, sinceit is recognized as inevitable that a relatively small but increasingamount of the desirable wax content will be taken from the wax stockwith the oil stream near the end of the de-oiling operation particularlyin the case of sweating when, of course, the wax stock in the sweaterhas been elevated in temperature to release the heavier undesired oils.Thus the operator can select that point in the operation at which thewax will possess just the desired properties for a finished wax productbut still will not be treated so long as to result in loss of product.

In the operation of the present process for sweating an oil-wax mixture,it has been found advantageous to provide a circulating stream of heatedwater through a plurality of relatively small pipes located throughoutthe tank type of sweater. Since it is desirable for the wax stock andthe temperature to be elevated slowly at a constant rate, it has beenfound that these desirable conditions may be obtained by providing anautomatic temperature control on the circulating stream of water. Thismay consist of a time-temperature controller which may actuate adiaphragm control valve which in turn governs the rate at whichpressurized and superheated steam is introduced into a circulatingstream of water. Thus the amount of superheated steam and thereby thetemperature of the circulating water may be gradually increased at aconstant predetermined rate with respect to length of time of processingor treatment. In this manner, substantially all of the lighterundesirable oils will be re moved before the progressively heavierundesirable oils are removed from the body of wax in the sweater. Inthis way a more effective sweating and uniform finished product may beobtained.

EXAMPLE A 3-gram sample of a crude parafiin wax known to have an oilcontent of 2 to 10% by weight is made into a cc. solution with pureiso-octane. The 100 cc. solution is poured into a clean, dry, tared 100cc. volumetric flask. The optical density or absorbance of the samplefor light having wavelengths within the range of 240 to 350millirnicrons is then determined with a spectrophotometer such as aBeckman Model DU Photoelectric Quartz Spectrophotometer in known manner.In the fol lowing table the values of A as defined heretofore weremeasured using an iso-octane solution of the stock at a concentration(0) of 2.907 grams of wax per liter and an optical path (0') in thespectrophotometer of 0.998 centimeter, the values of a were calculatedfrom the relationship described hereinbefore and the following resultswere obtained:

Table A Wavelength mu Absorbance Absorptivity 719 O. 248 701 0. 242 7010. 242 700 0. 241 701 0. 242 690 0. 238 669 0. 231 611 0. 210 534 0. 184447 O. 154 359 0. 123 262 0. 090 248 0. 086 251 0. 087 260 0. 090 263 0.091 262 O. 090 254 0. 088 244 0. 084 222 O. 077 194 0. 067 173 0. 060156 0. 054 142 0. 049 123 0. 042 108 0. 037 097 0. 033 051 0. 018 D38 0.013 028 O. 010 024 0. 008 020 0. 007 018 D. 006 018 0. 006

It was found that, for the crude wax thus tested, the curve obtained byplotting a values against Wavelength as illustrated in Fig. 1, had apeak absorptivity at 257 millimicrons. Similar tests with other samplesof wax from the same source showed that all waxes from that source had amaximum absorptivity at 257 millimicrons. Consequently, thedetermination thus far described need 'the u. v. oil content curve.

7 be made only once so long as the wax'sweated comes from the samesource. a s

' 'A commercial wax sweater was then filled with crude wax similar tothat of the sample and the sweating was carried out in the conventionalmanner. Samples of the foots oil were taken after 0, 4, 9, 14, 17, 20and 20% hours. The absorptivity values-of aliquot portions of thesesamples for light having a wavelength of 257 millirnicrons weredetermined in a Beckman Model 'DU Photoelectric QuartzSpectrophotometerin the same manner as previously described, andrecorded in column 2, Table I appearing hereinafter. The remainingportions of thesesamples were tested for correlation by the conventionalASTM testing methods to determine their oil content and the resultsrecorded in column 3 of Table I. The values thus obtained were plottedon logarithmic graph paper with the ASTM oil content in per cent as theordinate and the absorptivity (11257) as the abscissa.

The experiment was repeated on the same wax stock in two other tests andthe values recorded in Tables H and III hereinafter as columns 2 and 3respectively. These values were likewise plotted on Fig. 2 and the curveR drawn as shown. This curve R represents the mean of the points plottedof absorptivity versus ASTM oil content of the foots oil samples and isdesignated Due to the many factors which cause the ASTM calculations todigress slightly as explained before, the u. v. content values are ofgreater accuracy.

In addition in Tables I, II and III, there are included the observedabsorptivity of the wax and the ASTM oil 'content of the wax in thesweater at the cut points (the points at which the sweating isterminated). This absorptivity of the refined wax, when plotted againstthe ASTM oil content of the wax, gives the straight line curve R, whichis actually an extension of curve R.

' Curves R and R are joined and extended as shown in Fig. 2 to emphasizefurther the parallelism and identity of relationship between thecharacteristics of the foots oil strearn and the wax in the sweater.

Similarly the values from the curve R for the oil content of the wax inthe sweater represent the u. v. oil content of the wax and the valuesfor the wax at the cut points of the sweating runs is recorded in column5 of Tables I, II, and III, respectively. .These values are subject toless'error than the ASTM values from which they diifer slightly. p 1

When the u. v. oil content values of the wax in the sweater at the cutpoint (recorded in columns 5 of Tables I, II and III) is plotted againstthe absorptivity of the e-footsoil sample at the same point and a curveis drawn through the points, the curve T of Fig. 2"is obtained. Thiscurve T is fourid to be parallel to the curve R R' and to correlate theabsorptivit gi thesw e'atjstream with the oil content of the wax in th'ebody of the sweater at: the time the sweat stream sample wasobtai ned.The data above referred to in the Tables I, II and III areas follows:

Table II Foots Oil Refined Wax in Sweater Sweating U. V. Oil Con- Time,ASTM on tent g Hours G257 Oil am Content (calibfa- Content Content(curve tion (cam R) curve T) Table III Foots Oil Refined Wax in SweaterSweating U. V. Oil Con- Time, ASTM on tent Hours am Oil am ContentContent Content (curve tion (Cale R) curve T) Summarizing thisexplanation, the values in columns 2 and 3 are plotted to give the curveR; the values of columns 4 and 7 are plotted to give the curve R of Fig.2; the values in columns 5 of each table are plotted against theabsorptivity of the foots oil stream at the cut point (column 2) to givethe relationship represented by curve T, which is found to be parallelto R and R, differing by a constant factor which shifts the curve to theright on the graphic plot. Thus, the value of the oil content of wax inthe sweater may be determined at any time during the sweating operationby examining a sample of the foots oil at that time and the valuedetermined from curve T. These values for the Wax at the cut point areshown in columns 6 of Tables I, H and HI and it is seen how closely thevalues for oil content from curve T agree with the u. v. content shownin columns 5 of each table. In Table I, the value of the oil content inthe wax sweater is read from calibration curve T at each time the footsoil sample is examined. The successive values are recorded in column 6and are plotted against the time of sweating in Fig. 3. The value of oilcontent at 0 hour is not recorded as it differs but little from thatwhen temperature has been raised slightly at the end of 4 hours and thereading is more accurate after the sweating treatment has been inoperation a short time. The time-oil content relationships as recordedin Table I and plotted in Fig. 3 can be obtained for operations inTables H and III also, if desired.

In a subsequent operation, the values reported in Table IV below wereobserved. The absorptivity of the foots oil atthe cut point was observedto be 0.212 and the value .from the calibration curve (column 3)indicated that the oil content of the refined wax in the sweater at thispoint would be 0.86. This is close and within practical limits with theu. v. oil content value of 0.72 and even nearer the actual calculatedASTM value of 0.855 which is a difference of only 0.005 from the valueas determined from the. established calibration curve T. The agreementbetween values determined from the calibration curve and the actualvalues of the oil content of thewax is very close and well within apermissible difierence for all practical purposes. i

Table IV Refined Wax in Sweater Sweating Time, 0033311; 69 ASTM Hours(1257 (calibrae251 Content g tion (curve (c810 curve T) R) 3. 442 12.3 1. 854 6. 8 l. 010 3. 82 0. 718 2. 75 0. 432 1. 09 0. 306 l. 22 20 0.280 1'. 12 21% 0. 234 O. 95 Cut Point 22% 0. 212 0. 86 0. 664 07 72 O.855

The above example shows that the time to terminate the sweating in orderto obtain a wax product of proper properties, may be ascertained readilyby examining the absorptivity of a sample of the foots oil stream andreferring to the calibration curve T to determine if the wax has at thatpoint the desired and predetermined oil content to meet thespecifications.

The values of time at which foots oil samples were taken were recordedin column 1 and these values were plotted in Fig. 3 against the oilcontent of the wax in the sweater as it is determined (from calibrationcurve T) at each examination of a foots oil sample. From the resultingcurve (Fig. 3) it can readily be seen that, by extrapolating the curvebeyond values actually observed after several hours, it is possible todetermine approximately the time at which the sweating operation shouldbe terminated to yield a product of predetermined oil content as readalong the ordinate axis of the plot.

The preceding description has been described with special reference to acontrol of the sweating of oil-wax stocks to obtain a refined finishedwax of predetermined oil content by observance of the absorptivity ofsamples of foots oil from the sweater and reference to a calibrationcurve.

With slight modifications a difierent calibration curve may beestablished and a similar method of control obtained in solventde-oiling where the absorptivity of the oil removed from the oil-waxsample could be correlated with the oil content left in the wax and theoperation controlled by determining the absorptivity of successivesamples of solvent-removed oils and thereby observing the oil content ofthe wax.

It is evident that numerous modifications will immediately appear tothose skilled in the art upon reading the foregoing description. Allsuch modifications are intended to be included in the scope of theinvention as defined in the following claims.

We claim:

1. The method of preparing finished wax of a predetermined oil contentwhich comprises the steps of (l) sweating an oil-wax mixture, (2)withdrawing a sweat stream sample, (3) passing through said sampleultraviolet light of that wavelength between about 240 and 350millimicrons which corresponds to the characteristic absorptivity peakof said sample and noting the absorptivity value of the sample at thatwavelength, (4) repeating steps two and three until the absorptivity ofthe sweat stream sample reaches a value which corresponds to thepredetermined oil content of the wax Within the sweater as shown by apreestablished correlation between the oil content of the wax and theabsorptivity of the sweat stream sample, and (5) then immediatelyterminating the sweating.

2. A method according to claim 1 in which the predetermined oil contentof the wax is below 5%.

References Cited in the file of this patent UNITED STATES PATENTS2,386,831 Wright Oct. 16, 1945 2,406,210 Ferris Aug. 20, 1946 2,459,404Anderson Jan. 18, 1949 2,462,946 Coggeshall et al Mar. 1, 1949 2,462,995Ritzmann Mar. 1, 1949

1. THE METHOD OF PREPARING FINISHED WAX OF A PREDETERMINED OIL CONTENTWHICH COMPRISES THE STEPS OF (I) SWEATING AN OIL-WAX MIXTURE, (2)WITH-DRAWING A SWEAT STREAM SAMPLE, (3) PASSING THROUGH SAID SAMPLEULTRAVIOLET LIGHT OF THAT WAVELENGTH BETWEEN ABOUT 240 AND 350MILLIMICRONS WHICH CORRESPONDS TO THE CHARACTERISTIC ABSORPTIVITY PEAKOF SID SAMPLE AND NOTING THE ABSORPTIVITY VALUE OF THE SAMPLE AT THATWAVELENGTH, (4) REPEATING STEPS TWO AND THREE UNTIL THE ABSORPTIVITY OFTHE SWEAT STREAM SAMPLE REACHES A VALUE WHICH CORRESPONDS TO THEPREDETERMINED OIL CONTENT OF THE WAX WITHIN THE SWEATER AS SHOWN BY APREESTABLISHED CORRELATION BETWEEN THE OIL CONTENT OF THE WAX AND THEABSORPTIVITY OF THE SWEAT STREAM SAMPLE, AND (5) THEN IMMEDIATELYTERMINATING THE SWEATING.